The present invention relates to a printhead, head cartridge and a printer using the printhead and, more particularly, to a printhead and head cartridge for performing printing in accordance with an ink-jet printing method, and a printer using the printhead.
Increasing interest has been brought to the ink-jet printing method where printing is performed by discharging ink from small orifices (discharge orifices) onto a print medium such as fabric, paper, sheet material and the like, because the method provides various advantages: for instance, noise generated at the time of printing is so small that it can be ignored; high-speed printing is possible; printing is realized by fixing ink on so-called regular sheets of paper without any special processing.
A number of techniques have already been proposed as a method of ink-jet printing. For instance, the ink-jet printing method disclosed in Japanese Patent Application Laid-Open No. 54-51837 and German Publication (DOLS: Deutschland Offenlegungsschrift) No. 2843064, has a different feature from those of other ink-jet printing methods in the way that heat energy is given to liquid (ink) to generate driving force for ink discharge.
According to the printing method disclosed in each of the above-mentioned patent publications, the liquid activated by heat energy changes its state due to rapid increase in volume. Driving force generated by the change in the state causes discharging of the liquid from an orifice (discharge orifice) provided at the end of a printhead, forming a discharging droplet, and the droplet adheres to a print medium to form a pixel, thereby executing printing. In particular, the printing method disclosed in DOLS No. 2843064 is not only effectively applied to so-called drop-on-demand printing, but also contributes to easy manufacturing of a full-line type printhead, that is, a printhead having a size as large as the width of the print medium and having multiple orifices arrayed in line, and in addition, contributes to have the discharge orifices at high density. Accordingly, the printing method is advantageous in a way that an image having high resolution and high quality can be obtained at high speed.
The printhead of an ink-jet printing apparatus adopting aforementioned printing method is configured with: an ink nozzle comprising a discharge orifice provided to discharge an ink droplet and a liquid channel connected to the discharge orifice, and an element substrate of the printhead integrating an electrothermal transducer (heater) for generating heat energy. The liquid channel constitutes a part of a heating unit where heat energy acts on the liquid.
Since the printhead normally has plural discharge orifices, plural heaters are arrayed in line on an element substrate in correspondence with the discharge orifices. Furthermore, another type of element substrate of the printhead has been developed where the element substrate includes, in addition to the plural heaters arrayed in line, a driver provided in one-to-one correspondence with the heater for driving each of the heaters in accordance with image data, a shift register for parallelly outputting image data, which has been serially inputted, to each driver, and a latch circuit for temporarily storing the data outputted by the shift register. Normally, the element substrate is designed such that the number of bits of image data stored in the shift register is equal to the number of the heaters. For instance, if the number of heaters is 64 (the number of discharge orifices are 64), 64-bit shift registers are utilized.
The element substrate integrating the above-described circuits is manufactured by monolithically forming an IC (Integrated Circuit) having a Bi-CMOS structure (a structure including a bi-polar transistor and a CMOS transistor) on, e.g., a silicon substrate, and further forming a heater as a heating unit.
FIG. 6 is an equivalent circuit diagram showing an internal configuration of a logical circuit integrated in the element substrate of the conventional printhead having 64 ink discharge orifices. As shown in FIG. 6, the element substrate includes 64 heaters 101 (heating elements: H1, H2, . . . , H64) arrayed in one line, and power transistors 102 serving as drivers are provided in one-to-one correspondence with each heater 101. One end of each heater 101 is connected to a terminal 110 provided to supply power for driving heaters, and the other end is connected respectively to a collector of a corresponding power transistor 102. An emitter of the power transistor 102 is commonly connected to a common terminal 111.
The period of time each power transistor 102 is turned on is controlled in accordance with a pulse signal inputted to a heat-pulse-width input terminal 107. Image data (DATA) from an external unit is serially inputted (e.g., b1, b2, . . . b64) to a shift register 104 in a unit of one bit. In the output side of the shift register 104, a latch circuit 117 is provided. The shift register 104, connected to a clock input terminal 105 and a data input terminal 106, executes shift operation in accordance with a clock (CLK) inputted to the clock input terminal 105. In addition, on the element substrate, a power supply terminal 108 for supplying power to the logical circuit portion e.g., the shift register 104, latch circuit 117 and the like, and a ground terminal (GND) 109 are provided. The aforementioned elements are the minimal structural elements necessary for the logical circuit of the printhead.
It is a known fact in the ink-jet printhead that, by decreasing the number of discharge orifices which simultaneously discharge ink, it is possible to appropriately refill ink from an ink tank to a liquid channel, possible to prevent image quality from deterioration and possible to realize high-quality printing. Therefore, the logical circuit is designed such that the printhead is divided into a number of blocks (8 blocks in FIG. 6) so that adjacent discharge orifices do not simultaneously discharge ink.
To achieve the divided control, the logical circuit comprises input terminals 114, 115 and 116 where 3-bit block-selection signals (B2, B1 and B0) are parallelly inputted, a 3 to 8 decoder 118 for decoding the block-selection signals inputted to the input terminals 114 to 116 into a signal for each block, input terminals 112 and 113 where an odd-numbered-element selecting signal (hereinafter referred to as an ODD signal) and an even-numbered-element selecting signal (hereinafter referred to as an EVEN signal) are respectively inputted, and AND circuits 119 each corresponding to the respective power transistor 102. The logical circuit is designed such that the 64 power transistors are divided into 8 blocks each having 8 transistors, and that adjacent power transistors, that is, an odd-numbered element (H1, H3, . . . , H63) and an even-numbered element (H2, H4, . . . , H64), are separately driven, so that the number of transistors simultaneously driven is four at the maximum.
Four types of signals are inputted to each AND circuit 119. Each AND circuit 119 drives corresponding power transistor 102 on the basis of a logical AND of a signal (BLK1, BLK2, . . . , BLK8) outputted by the 3 to 8 decoder 118 for a corresponding block, a pulse signal (ENB) inputted to the heat-pulse-width input terminal 107, odd-numbered element or even-numbered element selecting signals (ODD or EVEN), and a signal outputted by the latch circuit 117.
For instance, if a block-selection signal B2 (MSB) is inputted to the input terminal 114, a block-selection signal B1 is inputted to the input terminal 115, and a block-selection signal B0 (LSB) is inputted to the input terminal 116 (where B2=B1=B0=0), an output signal BLK1 outputted by the 3 to 8 decoder 118 becomes "ON" and the heaters H1, H2, . . . , H8 are selected. Further, when an ODD signal is inputted to the input terminal 112, odd-numbered heaters H1, H3, H5 and H7 are selected.
Note that the power transistor 102 is formed by bi-polar process, and the logical circuit portion (shift register 104, latch circuit 117, 3 to 8 decoder 118 and AND circuit 119 and so on) is formed by CMOS process.
In the foregoing conventional example, as shown in FIG. 7A, a single connecting board 302 is sandwiched by two element substrates 301. Thus, to construct a printhead as shown in FIG. 7B, plural element substrates are arranged opposite to each other. Thus, referring to FIG. 7B, heaters on the upper element substrate are arrayed in the order of H1, H2, . . . from the left, while heaters on the lower element substrate are arrayed in the order of H1, H2, . . . from the right. In other words, the order of heaters' array is opposite for the upper and lower element substrates. Accordingly, a problem arises in that, when printing is performed with the printhead having the above-described configuration, in order to match the order of data input with the order of heaters' array, the order of inputting a block-selection signal from an external unit (printer) must be changed for the upper element substrate and the lower element substrate, or wiring for the upper element substrate or lower element substrate must be changed.
In order to solve the above problem, various improvement have been made on the construction of the element substrate of the printhead.
For instance, Japanese Patent Application Laid-Open No. 2-281973 discloses a printhead, comprising a driving IC for a case where the printhead is constructed with the identical-type element substrates arranged opposite to each other, to enable signal input from right to left or left to right of the heaters' array, so that the direction of signal input can be appropriately selected.
However, according to the printhead disclosed in Japanese Patent Application Laid-Open No. 2-281973, the number of signal terminals which are provided to enable bi-directional signal input is doubled. Therefore, since an element substrate even larger than the conventional size is required in order to implement the signal terminals on the element substrate, it is difficult to down-size the element substrate. This problem also causes increase in manufacturing cost of the apparatus. Moreover, the printhead integrates the heaters for heating ink to discharge ink droplets and the IC for driving the heaters on separate element substrates. Thus, down-sizing of the printhead is not easily realized. Furthermore, when terminals for inputting block-selection signals in the printhead are connected to corresponding terminals of a printer, the connection positions have to be changed, taking a direction of an element substrate into consideration. This results in complicated manufacturing process of the printhead.